1. Field of the Invention
This invention is in the field of equipment used to move switch points on a rail line, to direct movement of a rail vehicle along one track or another.
2. Background Art
Where two tracks of a rail line merge into a single track, it is necessary to have a switching mechanism to select which of the two merging tracks is to be aligned with the single track, for the desired routing of rail vehicles. Such a switching mechanism accomplishes this by moving a pair of rail ends called switch points, so that the two rails of the single track align with the two rails of one or the other of the two merging tracks. The switching mechanism can be driven by a reversible electric motor, which moves an operating rod or push rod linearly, in a direction transverse to the track rails, to move the switch points. The rotary motion of the electric motor shaft can be converted to this linear motion of the push rod by turning a threaded screw member, along which a traveling nut or block of some kind moves. As the traveling nut or block moves linearly along the screw member, it moves the push rod, to move the switch points. In addition to moving the switch points, the traveling nut will often incorporate a mechanism for de-energizing the motor at the ends of its travel, or for reversing the motor direction at those end points.
In addition to the electric motor, it is possible to provide a manual or emergency means for moving the switch points, in the event of a motor failure or a power failure. One type of manual mechanism for accomplishing this emergency switching operation is a hand crank mounted to the motor assembly. The hand crank can drive the threaded screw member, to move the traveling nut linearly along the screw member.
Such a switching mechanism must have durable components arranged in a robust construction, in order to withstand the heavy loads experienced by the rails and the attendant vibration, as well as surviving in the dirty, moist environment typically found along railroad tracks. Substantial forces are typically required to move the switch points, and the switching mechanism must reliably generate those forces without malfunction.